Medical devices including metallic films

ABSTRACT

Medical devices, such as endoprostheses, and methods of making the devices are disclosed. The medical device can include a composite cover formed of a deposited metallic film and one or more polymer layers. The polymer layers contribute to mechanical or biological properties of the endoprosthesis.

FIELD OF THE INVENTION

The invention relates to medical devices, such as endoprostheses, andmethods of making the devices.

BACKGROUND

The body includes various passageways such as arteries, other bloodvessels, and other body lumens. These passageways sometimes becomeoccluded or weakened. For example, the passageways can be occluded by atumor, restricted by plaque, or weakened by an aneurysm. When thisoccurs, the passageway can be reopened or reinforced, or even replaced,with a medical endoprosthesis. An endoprosthesis is typically a tubularmember that is placed in a lumen in the body. Endoprostheses can bedelivered inside the body by a catheter that supports the endoprosthesisin a compacted or reduced-size form as the endoprosthesis is transportedto a desired site. Upon reaching the site, the endoprosthesis isexpanded, for example, so that it can contact the walls of the lumen,e.g., adjacent the aneurysm. In some cases, the endoprosthesis is astent coated with a bioabsorbable polymer to decrease its porosity inthe short term.

The expansion mechanism may include forcing the endoprosthesis to expandradially. For example, the expansion mechanism can include the cathetercarrying a balloon, which carries a balloon-expandable endoprosthesis.The balloon can be inflated to deform and to fix the expandedendoprosthesis at a predetermined position in contact with the lumenwall. The balloon can then be deflated, and the catheter withdrawn.

In another delivery technique, the endoprosthesis is formed of anelastic material that can be reversibly compacted and expanded, e.g.,elastically or through a material phase transition. During introductioninto the body, the endoprosthesis is restrained in a radially compactedcondition. Upon reaching the desired implantation site, the restraint isremoved, for example, by retracting a restraining device such as anouter sheath, enabling the endoprosthesis to self-expand by its owninternal elastic restoring force.

SUMMARY OF THE INVENTION

The invention relates to medical devices, such as endoprostheses, andmethods of making the devices. Exemplary endoprostheses include stents,covered stents, and stent-grafts.

In some aspects, the invention relates to an endoprosthesis includingfirst and second tubular frameworks spaced apart by a degradable centralportion. The endoprosthesis defines an interior and an exterior. Incertain embodiments, the tubular frameworks are configured to exert aradially expansive force against a body passage sufficient to retain theendoprosthesis with respect to the body passage. The degradable centralportion can be configured to initially reduce a flow of blood betweenthe interior and exterior of the endoprosthesis and, subsequent todeployment, degrade over time providing increased flow of blood betweenthe interior and exterior of the endoprosthesis.

Another aspect of the invention relates to an endoprosthesis including agenerally tubular deposited metallic film defining first and second endsand at least one fenestration located between the ends. In general, theat least one fenestration has an area sufficient to pass amicrocatheter. A degradable layer initially obstructs the fenestration.Upon deployment of the endoprosthesis within a body passage, thedegradable layer degrades thereby opening the fenestration to provide anarea sufficient to allow passage of a microcatheter.

In some embodiments, the deposited metallic film includes nickel andtitanium. The film can have a thickness of less than about 50 μm.

Another aspect of the invention relates to an endoprosthesis defining aninterior and an exterior. The endoprosthesis includes a depositedmetallic film having a plurality of fenestrations and a degradablepolymer layer configured to reduce passage of liquid between theinterior of the endoprosthesis and the exterior of the endoprosthesisalong a path including the fenestrations. In some embodiments, the filmhas at least about 100 fenestrations. Upon deployment of theendoprosthesis within a body passage, the polymer layer typicallydegrades thereby allowing increased passage of fluid between theinterior of the endoprosthesis and the exterior of the endoprosthesisalong a path including the fenestrations.

Other aspects, features, and advantages of the invention will beapparent from the description of the preferred embodiments thereof andfrom the claims.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 a is a side view of an endoprosthesis in the radially expandedstate as deployed within a body passage adjacent an aneurysm. Theendoprosthesis has a plurality of polymer layers.

FIG. 1 b is a cross-section through the endoprosthesis of FIG. 1 a.

FIG. 2 a is a side view of a distal portion of a deployment device priorto radial expansion of the endoprosthesis.

FIG. 2 b is a side view of the distal portion of the deployment devicesubsequent to radial expansion of the endoprosthesis adjacent theaneurysm.

FIG. 3 a is a perspective view of an endoprosthesis having a pluralityof polymer layers.

FIG. 3 b is a cross-section through the endoprosthesis of FIG. 3 a.

FIG. 4 is a cross-section through an endoprosthesis.

FIG. 5 is a perspective view of an endoprosthesis.

FIG. 6 is a cross-section of an endoprosthesis.

FIG. 7 a is an endoprosthesis having a degradable central portion.

FIG. 7 b is the endoprosthesis of FIG. 7 a deployed in a body passagewith the central portion not yet degraded.

FIG. 8 a is an endoprosthesis with degradable portions.

FIG. 8 b is the endoprosthesis of FIG. 8 a deployed in a body passage. Amedical instrument is inserted through a degraded portion of theendoprosthesis.

FIG. 9 a is an endoprosthesis having a cover having a plurality ofmovable plates.

FIG. 9 b illustrates a radially compressed configuration of severalplates of the endoprosthesis of FIG. 9 a.

FIG. 9 c illustrates a radially expanded configuration of several platesof the endoprosthesis of FIG. 9 a.

FIG. 10 a is cover with a metallic film defining fenestrationsconfigured to have minimal stress in a radially compressed state.

FIG. 10 b illustrates the cover of FIG. 10 a in a state of radialcompression about midway between the radially compressed state of FIG.10 a and a fully expanded state.

FIG. 10 c illustrates the cover of FIG. 10 a in a state of radialexpansion about that assumed in a body passage.

FIG. 11 is a cover with a metallic film defining fenestrationsconfigured to have minimal stress in a radially expanded state within abody passage.

DETAILED DESCRIPTION

Referring to FIGS. 1 a and 1 b, an endoprosthesis 100 is deployed withina body passage, e.g., within a vessel weakened by an aneurysm, e.g., ananeurysm 25 of a vessel 26 of a human brain. Endoprosthesis 100 includesa framework, e.g., a stent body 52, covered by a tubular member or cover54, which are secured to one another by polymer layers 101. The stentbody provides a relatively rigid framework that secures theendoprosthesis at the treatment site. The framework defines relativelylarge openings or fenestrations that contribute to the mechanicalproperties of the stent. The cover 54 is relatively thin and flexibleand includes smaller fenestrations that contribute to the mechanicalproperties of the cover 54 and can occlude the fenestrations of thestent.

The endoprosthesis 100 modifies an amount or velocity of blood passingbetween vessel 26 and aneurysm 25. For example, prosthesis 100 can bedeployed to divert, reduce or block blood flow between vessel 26 andaneurysm 25. The endoprosthesis can also reduce blood flow betweenvessel 26 and a feeder vessel 27. If so deployed, prosthesis 100 maysufficiently reduce blood flow to allow clotting or other healingprocesses to take place within aneurysm 25 and/or opening 29. Tubularmember 54 can provide a greater attenuation of the blood flow into theaneurysm 25 than stent body 52 alone. Endoprosthesis 100, however, canallow some flow to pass between vessel 26 and aneurysm 25 even whileproviding flow diversion and/or reduction in flow. Prosthesis 100 canalso (or alternatively) allow blood to pass between vessel 26 containingthe prosthesis and adjacent vessels, e.g., feeder vessel 27, while stillproviding reduced flow with respect to the aneurysm.

Referring to FIGS. 2 a and 2 b, endoprosthesis 100 is deployed toaneurysm 25 using a deployment device 30, such as a catheter that can bethreaded through a tortuous anatomy. The device 30 includes aretractable outer sheath 31 and an inner catheter 32. Device 30 isintroduced over a guide wire 37 extending along the interior 28 ofvessel 26. During introduction, the endoprosthesis 100 is radiallycompacted between outer sheath 31 and inner catheter 32 adjacent adistal opening 40 of the outer sheath.

Referring particularly to FIG. 2 b, the outer sheath 31 is retractedupon reaching the desired deployment site, e.g., aneurysm 25. In someembodiments, endoprosthesis 100 self-expands by its own internal elasticrestoring force when the radially restraining outer sheath is retracted.Alternatively, or in combination with self-expansion, deployment ofprosthesis 100 may include use of a balloon or other device to radiallyexpand prosthesis 100 within vessel 26. After deploying theendoprosthesis, the inner catheter 32 and guide wire 37 are withdrawnfrom vessel 26. Suitable delivery systems include the Neuroform,Neuroform2, and Wingspan Stent System available from Boston ScientificTarget Therapeutics, Fremont, Calif. In embodiments, the outer sheathand/or inner catheter includes a reinforcing member to respectivelyresist elongation or compression as the outer sheath is withdrawn. Suchreinforcing members include polymer shafts, braids, and coil structures.

Upon expansion, the endoprosthesis assumes a shape and radial extentgenerally coextensive with an inner surface of the vessel 26, e.g., atubular shape centered about a longitudinal axis a1 of the prosthesis(FIG. 1 a). Depending upon the application, prosthesis 100 can have adiameter d of between, for example, 1 mm to 46 mm. In certainembodiments, a prosthesis for deployment within a vessel at an aneurysmcan have an expanded diameter d of from about 2 mm to about 6 mm, e.g.,about 2.5 mm to about 4.5 mm. Depending upon the application, prosthesis100 can have a length along axis a1 of at least 5 mm, at least 10 mm,e.g., at least about 30 mm. An exemplary embodiment has an expandeddiameter of about 3.5 mm and a length of about 15 mm. In embodiments,the stent body has a closed cell framework, an open cell framework, ahelical framework, a braided framework, or combination thereof.

The cover can be fixed to the stent by, e.g. fasteners. Attachmenttechniques include brazing, welding or attachment with a filament,rivets or grommets, or crimping, or adhesive. In some embodiments, thetubular member differs from a fabric at least in that the tubular memberlacks fibers that can be pushed apart to receive a filament as by sewinga fabric. Accordingly, the fenestrations can be formed prior to theprocess of passing the filament through the tubular member.Fenestrations that receive the filaments can be formed by, e.g.,etching, laser cutting, or a photolithographic process. Attachmenttechniques are described in U.S. Ser. No. 11/025,866, titled MEDICALDEVICES INCLUDING METALLIC FILMS AND METHODS FOR MAKING SAME, filed Dec.29, 2004 and incorporated herein by reference.

The cover is formed of a thin film that exhibits advantageous propertiessuch as strength, toughness, and flexibility by selection of thecomposition of the film, processing techniques, and mechanicalconfiguration. For example, in particular embodiments, the film is avapor-deposited material composed of a nickel-titanium alloy having astrength additive, e.g. chromium. The film has a thickness of about 50μm or less, e.g. about 4-35 μm, and includes fine fenestrations, whichfacilitate collapsing the film to small diameter for delivery into thebody and expansion at the treatment site, while impeding blood access tothe aneurysm. In some embodiments, the film has at least about 100fenestrations, e.g., at least about 250 fenestrations. In particularembodiments, the film is processed to modify dislocations, whichcontribute to strength and toughness of the thin film.

Deposited materials, e.g., metallic films, are formed by depositing filmconstituents from a suspended state, e.g. in a vapor or a vacuum onto asurface. In embodiments, the constituents are suspended, e.g. bybombarding, heating or sputtering a bulk target. The suspendedconstituents deposit on a substrate to form the film. Deposited filmscan exhibit highly uniform thickness and microstructure in very thinfilms, e.g. about 50 μm or less, e.g. 4-35 μm. Deposition techniquesinclude sputter deposition, pulsed laser deposition, ion beam depositionand plasma deposition. Suitable deposition processes are described inBusch et al. U.S. Pat. No. 5,061,914, Bose et al. U.S. Pat. No.6,605,111, Johnston U.S. Pat. No. 6,533,905, and Gupta et al. U.S.2004/0014253, the entire contents of all of which are herebyincorporated by reference.

In particular embodiments, the deposited film is an alloy that includesnickel and titanium, and a strength additive or additives, which modifya mechanical property, e.g., a hardness or elasticity, of the film. Inparticular embodiments, the film is a tertiary alloy that hassubstantially no other components besides nickel, titanium, and additivepresent in an amount greater than 1%, 0.5% or 0.1% or less than 20%,10%, or 5% by weight of the film. The film may consist essentially ofnickel, titanium, and chromium. In embodiments, the deposited filmincludes between 54 and 57 weight percent nickel with the balancecomposed essentially of titanium and chromium. In some embodiments, aratio of a weight of chromium of the film to a combined weight ofnickel, titanium, and chromium of the film is at least 0.001, at least0.002 e.g., at least 0.0025. The ratio of the weight of chromium of thefilm to the combined weight of chromium, nickel, and titanium of thefilm can be 0.02 or less, 0.01 or less, e.g., 0.0075 or less. The ratioof the weight of chromium to the combined weight of chromium, nickel,and titanium of the film can be about 0.0025. In embodiments, the alloyexhibits superelastic or pseudo-elastic properties. Superelastic orpseudo-elastic metal alloy, as described, for example, in Schetsky, L.McDonald, “Shape Memory Alloys,” Encyclopedia of Chemical Technology(3rd ed.), John Wiley & Sons, 1982, vol. 20. pp. 726-736; and commonlyassigned U.S. Ser. No. 10/346,487, filed Jan. 17, 2003.

A cover of deposited metal film contributes to desirable properties ofan endoprosthesis. For example, as discussed above, cover 54 contributesto a flow diversion or reduction function. In some embodiments, aconfiguration and mechanical properties of the metallic film enhance theability of the cover to withstand significant radial compression duringdeployment yet provide desirable properties in situ. An endoprosthesiscan also include polymer layers, which, alone or in cooperation with acover, contribute to properties of the endoprosthesis. Some polymerlayers provide a mechanical function such as by securing a cover andstent body together or modifying surface properties of a metallic film,e.g., a lubricity or a roughness thereof. In embodiments, a polymermodifies a radial force exerted by the endoprosthesis against a bodypassage. Some polymers lend biological functionality to theendoprosthesis. For example, a polymer may improve biocompatibility,enhance cell growth, or provide a pharmacological function, e.g.,release of a therapeutic agent. In some embodiments, a polymer of anendoprosthesis degrades with time modifying mechanical and/or biologicalproperties of the endoprosthesis. Embodiments of endoprosthesesincluding covers having a metallic film are now described.

Returning to FIGS. 1 a and 1 b, polymer layers 101 have a pattern thatgenerally aligns with portions of the stent body, e.g., frameworkmembers 58,59 of the stent body. FIG. 1 b shows that polymer layers 101envelope members 58 and cover 54. A securing function is provided bymechanical properties of the polymer, which prevent the stent body andcover from tearing completely apart. Despite securing the stent body andtubular member, polymer layer 101 can allow some relative movementbetween the stent body and tubular member. In embodiments, relativemovement occurs during radial compression and expansion and providestolerance for some differential length changes, e.g., foreshortening,between the stent body and tubular member.

Polymers can be selected to provide desirable mechanical or chemicalproperties. For example, highly elongatable or elastic polymers ratherthan rigid polymers can be used to allow relative movement between astent body and cover. In some embodiments, a layer of the polymer canhave an elongation at break of at least 500%, at least 800%, at least900%, or at least 1000%. A layer of the polymer can have a tensilemodulus of at least 10,000 psi, at least 50,000 psi, or at least 75,000psi. A layer of the polymer has a tensile strength of at least 2,500psi, at least 5,000 psi, at least 7,500 psi, or at least 10,000 psi.

In some embodiments, the polymer includes or is formed of a butyric acidderivative polymer, e.g., poly-4-hydroxybutyrate,poly-4-hydroxybutyrate, orpoly-(3-hydroxybutyrate-co-4-hydroxybutyrate). The butyric acidderivative polymer film may have a tensile strength of at least about7,500 psi, a tensile modulus of about 10,000 psi, and an elongation atbreak of about 1,000%. Exemplary butyric acid derivative polymers areavailable from Tepha, Inc. of Cambridge, Mass. and include TephELAST₃₁,and TephaFLEX. Such butyric acid derivative polymers can provide betterelongation and strength than polytetrafluorethylene while also providingan amount of lubricity.

The polymer can include a urethane alone or in combination with one ormore additional polymers, e.g., as a copolymer. Exemplary urethanesinclude, e.g., biodegradable urethanes such as bone cement,polyurethane, dispersions and/or emulsions including aqueous dispersionsand/or emulsions such as NeoRez R-985 (aliphatic polycarbonate diol),NeoRez R-986 (aliphatic polycarbonate diol) from Astra-Zeneca, W830/048(polycarbonate backbone), W830/092 (modified polycarbonate backbone),W830/140 (polycarbonate backbone) and W830/256 (polycarbonate backbone),from Industrial Copolymer Ltd., Bayhydrol 121 (anionic dispersion of analiphatic polycarbonate urethane polymer in water andn-methyl-2-pyrrolidone with a tensile strength of 6,700 psi and anelongation at break of 150%) and Bayhydrol 123 (anionic dispersion of analiphatic polycarbonate urethane polymer in water andn-methyl-2-pyrrolidone with a tensile strength of 6,000 psi and anelongation at break of 320%) from Miles Inc. (Bayer AG).

In some embodiments, the polymer includes both urethane and silicone,e.g., a polyurethane/silicon copolymer. Such polymers can be highlycompressible and exhibit elongations before break of 400% or more.Polyurethane/silicon copolymers tend to provide good adherence to theendoprosthesis. Exemplary silicone-polyurethane copolymers include theElast-Eon series of polymers, e.g., Elast-Eon 2A, Elast-Eon 2D,Elast-Eon 3A, Elast-Eon 3LH and Elast-Eon HF polymers, available fromAortech of Victoria, Australia.

Other exemplary polymers include, e.g., biocompatible, non-porous orsemi-porous polymer matrices made of a fluoropolymer, e.g.,polytetrafluoroethylene (PTFE) or expanded PTFE, polyethylene, naturalnylon, aqueous acrylic, silicone, polyester, polylactic acid, polyaminoacid, polyorthoester, polyphosphate ester, polypropylene, polyester, orcombinations thereof.

In some embodiments, polymer layer 101 includes a biodegradable polymer.Exemplary biodegradable polymers include natural nylon, polysaccharidessuch as for example, methyl cellulose, hydroxymethyl cellulose,hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxy-propylmethylcellulose, hydroxpropylethyl cellulose, sodium carboxymethyl cellulose,hyaluronic acid, chondroitin sulfate, chitosan, dextran, xanthan,gellan, alginic acid, jota carrageenan; polypeptides such as forexample, collagen, gelatin, elastin, albumin; and synthetic polymerssuch as for example, poly(vinyl alcohol), poly(lactic acid),polyglycolic acid, polycaprolactone, polyanhydride, ethylene vinylacetate (EVA) their copolymers and mixtures thereof.

In some embodiments, degradation of polymer layer 101 is accompanied bythe release of a pharmaceutically active compound, e.g., a therapeuticagent or drug. Polymers providing such a release function are describedin U.S. Pat. No. 5,674,242, U.S. Ser. No. 09/895,415, filed Jul. 2,2001, and U.S. Ser. No. 10/232,265, filed Aug. 30, 2002. The therapeuticagents, drugs, or pharmaceutically active compounds can include, forexample, anti-thrombogenic agents, antioxidants, anti-inflammatoryagents, anesthetic agents, anti-coagulants, and antibiotics. Release canalso occur without substantial or any degradation of the polymer.

Polymer layers 101 can be formed by contacting a cover and stent bodywith a flowable or sprayable polymer, such as by dip coating or spraycoating. Upon curing, the polymer provides functionality, e.g.,securement, to the endoprosthesis. In some embodiments, significantportions, e.g., all of a length of an endoprosthesis are contacted withpolymer. Subsequently, portions of the polymer are removed, e.g., bylaser ablation after curing. Polymer can be removed quite selectively ifdesired. For example, a polymer that initially occludes fenestrations ofa cover can later be removed from some or all of the fenestrations whileleaving polymer surrounding the fenestrations. In other embodiments,portions of the cover or stent body are protected from contact with thepolymer, e.g., by a mask or temporary coating.

An endoprosthesis can include polymer layers configured differently fromlayers 101 to provide a securing function or other mechanical orbiological functionalities. Referring to FIGS. 3 a and 3 b, anendoprosthesis 120 includes a stent body 121 surrounded by a cover 123.Two polymer end portions 127, 129 and a polymer central portion 131extend generally circumferentially without following particular elementsof the stent body.

In some embodiments, end portions 127, 129 are located within the cover.As seen in FIG. 3 b polymer layer 129 provides a securing function byadhering to an inner surface 157 of the cover. Polyurethane-siliconecopolymers exhibit suitable adhesion properties yet allow some freedomof movement between the stent body and cover to tolerate differentiallength changes upon compression-expansion. Framework members 58 of astent body are enveloped by the polymer layer, which, in thecross-section shown, is not present on an external surface of theprosthesis. Film 123 does not include fenestrations in the cross sectionshown and may include no fenestrations at all. In alternativeembodiments, the stent body surrounds the cover with the polymer layerenveloping portions of the stent body and adhering to an externalsurface of the cover.

In some embodiments, end portions 127, 129 have a sufficient thicknessand material properties to increase (or decrease) a radial expansiveforce exerted by the end portions of the endoprosthesis. As seen in FIG.1 a, end portions of a deployed endoprosthesis engage vessel walls toeither side of an aneurysm. Radial force exerted by the ends of theendoprosthesis prevents movement along the vessel without damaging thevessel walls. Polymer layers 127, 129 can cooperate with a stent bodyand cover to provide an appropriate level of radial force, such as byresisting expansion of the stent body.

Polymer end portions 127, 129 have respective widths w1, w2, which maybe at least about 10% of the length of the endoprosthesis, e.g., atleast about 20%, at least about 40%, e.g., at least about 60% of thelength. The widths w1, w2 may be different. One of the polymer endportions is not be present in some embodiments. In some embodiments,polymer end portions are 25 μm thick or less, 20 μm thick or less, 15 μmthick or less, or 10 μm thick or less. The polymer can be formed of aplurality of individual layers, each having a thickness less than thetotal thickness of the polymer. For example, the polymer can be formedof a plurality of layers each having a thickness of 5 μm or less or 2 μmor less.

The central polymer portion 131 has a width w3 configured to straddle ananeurysm or other treatment site. In some embodiments, central polymerportion 131 provides a flow diversion or reduction function that cancooperate with fenestrations 133 of the cover. For example, polymerportion 131 may include a degradable polymer layer that initiallyoccludes fenestrations 133 of the cover by an amount sufficient tofurther limit or prevent liquid, e.g., blood, from passing between aninterior of the endoprosthesis (e.g., from within a vessel in which theendoprosthesis is disposed) and an exterior of the endoprosthesis (e.g.,into an aneurysm adjacent the endoprosthesis). Because the polymer isdegradable, the further limitation or occlusion of flow is temporary.The degradation of the layer, e.g., over weeks, months, or years, opensthe occluded fenestrations 133 allowing increased passage of fluidthrough the previously occluded regions. The central polymer portion mayalso release drugs or other therapeutic agents. Of course, a polymerlayer can be used to permanently occlude fenestrations of a cover.

In some embodiments, polymer end portions 127, 129 are located externalto cover 123 and include a topography or chemical properties configuredto enhance long-term engagement of the endoprosthesis and the vesselwalls adjacent the treatment site. For example, the topography of theouter surface of the polymer layers can include a plurality of poreshaving a size sufficient to enhance cell in-growth. The polymer releasescompounds to enhance such growth. The central polymer portion may alsorelease drugs or other therapeutic agents.

Referring to FIG. 4 an endoprosthesis 160 includes a composite covercomprising an interior polymer layer 159, a metallic film layer 154, andan exterior polymer layer 161. The composite cover surrounds a stentbody with framework members 58. Layers 159, 161 can be formed from aflowable composition of the polymer. In other embodiments, the metallicfilm is deposited, e.g., by vapor deposition, directly onto one ofpolymer layers 159 or 161. A polymer layer may itself be deposited froma vapor onto the metallic film. Alternative composites are alsopossible. For example, the layers may be reversed so that a polymerlayer is sandwiched by two metallic layers.

Referring to FIG. 5, an endoprosthesis 275 includes a patterned polymerlayer 278, which modifies a radial force exerted by a stent body 277 andcover 154 of the endoprosthesis. Patterned polymer layer 278 is formedof a plurality of polymer strands 279 extending circumferentially withrespect to the endoprosthesis 275. Each strand 279 defines a helixencircling an exterior of a cover 154. Strands defining opposedorientations cooperate to define a lattice structure of the patternedlayer 278.

Strands 279 may be oriented fibers of a polymer having a high tensilemodulus and tensile strength. In some embodiments, the strands areoriented fibers of a butyric acid derivative having a tensile modulus ofat least 100,000 psi and a tensile strength of at least about 70,000psi. Oriented fibers of TephaFLEX available from Tepha, Inc. areexemplary. The oriented fibers can guide and constrain radial expansionof the endoprosthesis. In such embodiments, the maximum expandeddiameter of the deployed endoprosthesis may be less than a diameterattained in the absence of pattern 278.

Strands 279 may be formed of a polymer having a highly compressiblepolymer having a high elongation before break. Urethane-siliconecopolymers such as from the Elast-Eon series of polymers from Aortechcan provide such properties. For example, a polymer Elast-Eon 3LH fromAortech has a tensile modulus of about 1,000 psi and an elongationbefore break of about 650%. Such highly compressible and elongatablepolymers can contribute positively to a radial force exerted by theendoprosthesis.

The polymer pattern 278 can be formed by spin coating strands 278 suchas by extruding a polymer through a nozzle and rotating theendoprosthesis with respect to the nozzle. The extruded strands 279typically have a thickness of about equal to or less than cover 154. Insome embodiments, strands 279 may have a diameter of about 10 μm orless, e.g., about 2 μm or less.

The polymer bands can have a thickness less than that of the tubularmember. For example, the polymer bands can be about 50% of a thicknessof a thin film of the tubular member.

Although pattern 278 is shown disposed about an entire length of cover154, a central portion, e.g., at least a central 30%, 40%, 60%, 80%, or90% of the endoprosthesis 275 may lack a polymer pattern sufficient tosubstantially modify a radial expansive force of the endoprosthesis. Forexample, a central portion of the endoprosthesis can include a polymerthat contributes to other properties, e.g., lubricity, fenestrationocclusion, or therapeutic agent delivery without substantially alteringa radial expansive force of the endoprosthesis.

Referring to FIG. 6, an endoprosthesis 175 seen in cross-sectionincludes a stent body having framework members 58 and cover 54 envelopedby a polymer layer 177, which provides a smoother outer surface than anuntreated, deposited metallic film. Compared to the untreated film, thepolymer layer 177 can have a smoother topography, an increasedlubricity, a lower surface energy, improved mechanical properties, e.g.,improved stretchiness or tear resistance, or combination thereof. Forexample, outer portions 179 of the cover 54 exhibit a lower coefficientof friction when translated with respect to the inner surface of asheath used to deploy the endoprosthesis. Hence, during deployment, lessforce is required to begin withdrawing the sheath from the radiallycompressed endoprosthesis. In the embodiment shown, fenestrations 62 ofcover 54 are not occluded by layer 177, which has a smaller thicknessthan the cover. For example, layer 177 may have a thickness of a fewmicrons or less.

Referring to FIG. 7 a, an endoprosthesis 325 includes a biodegradablecenter portion 326, which can be used to temporarily occlude a site,e.g., an aneurysm, and later provide increasing flow or access to thesite. Center portion 326 is disposed between two stent bodies 327 eachhaving an outer end 330 and an inner end 331. Center portion 326 issecured between inner ends 331 of stent bodies 327. For example, innerends 331 may include struts 332, which crimp about outer edges 333 ofcenter portion 326. Radiopaque markers 334 define boundaries betweeninner ends 331 of stent bodies 327 and outer edges 333 of center portion326.

With reference to FIG. 7 b, endoprosthesis 325 is deployed within a bodypassage, e.g., to a site of aneurysm 25. Markers 334 are visualized toposition endoprosthesis 325 so that outer edges 333 of center portion326 straddle opening 29 of aneurysm 25. The endoprosthesis is deployedas described above. Upon deployment, center portion 326 limits orprevents flow of blood between interior 28 of vessel 26 and aneurysm 25.Center portion 326 may include fenestrations so as not to restrict bloodflow entirely. Hence, center portion 326 may allow flow between feeder27 (if present) and vessel interior 28.

Over time following deployment, e.g., weeks, months, or even severalyears, center portion 326 degrades. In embodiments, the entirety ofcenter portion 326 is composed of degradable material so that, uponcomplete degradation, only endoprosthesis portions upstream anddownstream of markers 334 remain intact within vessel 26. Thedegradation provides increased flow between interior 28 of vessel 26 andsites, e.g., aneurysm 25, once occluded by center portion 326.Degradation of the central portion 326 can be accompanied by release ofa pharmaceutically active compound.

In other embodiments, center portion 326 includes a biodegradableportion and another portion, which is either not biodegradable or has asignificantly different degradation lifetime. For example, prosthesis325 may include markers that allow circumferential positioning of theprosthesis with respect to aneurysm 25 and feeder vessel 27. A firstportion of center portion 326 has a short degradation lifetime and isoriented to face feeder 27. A second portion of center portion has alonger degradation lifetime as is oriented to face aneurysm 25.Accordingly, prosthesis 325 can provide both rapid reestablishment offlow between a vessel weakened by an aneurysm and a vessel branchingtherefrom and long-term flow reduction with respect to the aneurysmitself.

Stent bodies 327 may, e.g., be surrounded by, tubular members 329,which, except for being shorter, may have properties of tubular membersdiscussed herein. For example, the tubular members 329 may each includea thin film, such as a metallic film. In some embodiments, tubularmembers 329 increase a surface area of endoprosthesis 325 as compared toa surface area if the members were not present. The increased surfacearea can enhance the longitudinal fixation of the prosthesis withrespect to vessel 26, especially upon degradation of center portion 326.Tubular members 329 can include coating that enhances cell in growthwith respect to the members. In some embodiments, a metallic filmextends between and connects tubular members 329. In some embodiments,tubular members 329 are only connected by center portion 326.

In some embodiments, the endoprosthesis lacks one or both of the stentbodies. Instead, the outer edges 333 of center portion 326 can each beinitially secured to a tubular member 329 having sufficient thickness,e.g., at least 35 μm, to exert a securing radial force. The centerportion and tubular members 329 are joined by, e.g., crimping. Upondegradation of the center portion, all that may remain is the tubularmembers and markers, if present. In some embodiments, the tubularmembers are connected by struts or portions of the tubular member thatextend across center portion 326.

Referring to FIGS. 8 a and 8 b, an endoprosthesis 350 includes a tubularmember 351 having plurality of fenestrations 353, which are initiallyoccluded by a degradable layer 354. In use, endoprosthesis 350 isdeployed so that occluded fenestrations 353 are aligned with a treatmentsite, e.g., aneurysm 25. Initially, degradable layer 354 obstructspassage between interior 28 of vessel 26 and locations external thereto,e.g., aneurysm 25. Subsequent to deployment, layer 354 degrades and mayopen fenestrations 353 entirely. Fenestrations 353 can be large enoughto provide passage for an instrument, e.g., a catheter, to extend frominterior 28 of vessel 26 at least to opening 29 of aneurysm 25 andperhaps even further therein (FIG. 8 b). For example, fenestrations 353can be at least large enough to provide passage for a 1.7 frenchcatheter 360. The fenestrations 353 can have an unobstructed area of 2mm2 or more. In some embodiments, degradable layer 354 itself includesfenestrations, which may allow for some flow therethrough even when thelayer is not yet degraded.

In some embodiments, endoprosthesis 325 includes an array offenestrations 353 as shown. In other embodiments, the endoprosthesisincludes only a few or even one circumferential fenestration. Theendoprosthesis can include markers that are indicative of acircumferential orientation of the fenestrations. Hence, thefenestrations 353 can be aligned not only longitudinally with respect toaneurysm 25 but circumferentially with respect to opening 29 or feeder27.

Referring to FIG. 9 a, an endoprosthesis 300 includes a tubular member301 having a plurality of plates 303, which spread apart upon radialexpansion of the endoprosthesis. Because of the expansion, tubularmember 301 can be radially compressed to a small diameter and thenradially expand upon deployment to provide a substantially greatersurface area than in the absence of spreading plates 303. Accordingly,endoprosthesis 300 can be delivered within a radially compact deliverydevice yet conform to the wall of a relatively larger diameter vesselupon deployment.

A central portion 307 of tubular member 301 includes a plurality ofplates 303 connected by struts 304. A stent body 302 supports plates 303and end portions of the tubular member. Adjacent plates 303 areseparated by gaps 306 through which framework members 305 of stent body302 can be seen. In other embodiments, the stent body does not extendbetween opposite ends of the endoprosthesis. Instead, two independentstent bodies provide a radial outward force to secure the prosthesis ina vessel.

Referring also to FIG. 9 b, adjacent plates 303 overlap whenendoprosthesis 300 is radially compressed as for delivery along a bloodvessel to an aneurysm site. Referring to FIG. 9 c, plates 303 spreadapart upon radial expansion increasing the effective surface area ofcentral portion 307. Arrows 308 illustrate generally the relativemovement of adjacent plates 303. Because plates 303 overlap whenradially compressed and spread apart when radially expanded, centralportion 307 tubular member 301 can define a greater surface area thanwould otherwise be possible without significantly changing the surfacearea of plates 303 themselves.

In some embodiments, at least 10%, at least 25%, at least 35%, at least50%, or at least 70% of plates 303 are overlapped in the radiallycompressed state. Hence, the apparent surface area of endoprosthesis 300can be significantly larger in the expanded state than in the radiallycompressed state. In some embodiments, 30% or less, 20%, or less, e.g.,10% or less of plates are overlapped in the radially expanded state.Some degree of overlap between plates can help limit a tendency of aplate to flex radially outwards or inwards in response to blood flowinternal to or external to the deployed prosthesis. For example, a tip310 of a plate can overlap or be overlapped by a base 311 of anotherplate (FIG. 9 c).

A deposited metallic film can contribute desirable mechanical propertiesto plates and struts of the cover. For example, tubular member 300 caninclude a thin film, e.g., metallic film comprising nickel, titanium,and, optionally, a strength additive, e.g., chromium. An amount ofstrength additive may vary in different portions of the film. In someembodiments, elbows 309 include a different amount of strength additivethan plates 303.

Plates and struts including a deposited metallic film can be formed withminimal thickness, e.g., about 50 microns or less, e.g., about 4 toabout 35 microns. Struts 304 can include elbows 309 defining significantbends, e.g., 130° or more, 150° or more, or 180° or more. Elbows 309 canhave a composition and/or cross-section different from plates 303. Insome embodiments, elbows have a circular or oval cross-section whereasas plates 303 are substantially planar.

Referring to FIG. 10 a, a metallic film 260 useful as a cover of anendoprosthesis includes a plurality of fenestrations 261 having minimalstress when radially compressed within a delivery device. Minimizingstress in the radially compressed state can reduce or preventdeformation, e.g., warping or kinking, of the film. Upon radialexpansion, the fenestrations 261 may experience a relatively greaterstress than an alternative fenestration configuration. However, becauseforces experienced by the radially expanded film tend to be moreuniform, the film can tolerate radial expansion without deformation.

In a relatively unexpanded state (FIG. 10 a), each fenestration 261includes a plurality of parallel walls extending along a majorfenestration axis a1, which is parallel to a longitudinal axis a2 of anendoprosthesis that would receive the film 260 as a cover. Ends 263 ofeach fenestration are arcuate. Upon partial radial expansion (FIG. 10b), interior walls 265 adjacent the ends 263 spread apart defining anon-parallel angle α with the longitudinal axis a2. A pair of centrallylocated walls 267 remain parallel to one another. Accordingly, eachfenestration 261 assumes a hexagon shape.

In a fully expanded state (FIG. 10 c), e.g., at vessel size, walls 265spread further apart and each fenestration 261 assumes an elongatedhexagon having a major axis a3 aligned with a circumferential axis ofthe endoprosthesis. Walls 267 remain parallel to one another despite thecircumferential elongation.

Referring to FIG. 11, a metallic film 270 useful as a cover of anendoprosthesis includes a plurality of struts 275, which definefenestrations 271 having minimal stress when radially expanded within abody passage, e.g., a vessel. In an unexpanded state, as shown,fenestrations 271 have a diamond shape defining a minor axis a5 and amajor axis a4, which is aligned with a longitudinal axis of anendoprosthesis including the cover. A ratio (in the unexpanded state) ofthe major axis a4 to the minor axis a5 may be about 6 or less, about 5or less, e.g., about 3 or less. A width w4 of metallic film struts 275may be about 50 μm or less. A thickness of the film along a dimensionnormal to the film is less than the thickness of the struts and may beabout 15 μm or less.

In addition to selecting a fenestration configuration that minimizesstress at a particular radial dimension, a cover can be shape set at aselected radial dimension. This shape set radial dimension may or maynot match the radial dimension that minimizes stress of thefenestrations. A film can be shape set by, for example, setting the filmat the selected radial dimension and heating the film to, e.g., about500° C. In some embodiments, the film is shape set at a diameter aboutthe same as or somewhat larger than an inner diameter of a deliverydevice sheath that surrounds the tubular member during implantation. Inanother embodiment, the film is shape set at a diameter about the sameas or somewhat smaller than the inner diameter of a body passage toreceive an expanded endoprosthesis. A stent body used with the cover mayalso be shape set to a selected radial dimension. A ratio of the shapeset diameter of the cover 54 to the expanded diameter of stent body 52in the absence of tubular member 54 may be about 1 or less, about 0.95or less, or about 0.9 or less.

In other embodiments, a deposited metallic thin film and one or morepolymer layers are useable as an endoprosthesis without a supportingstent. For example, an endoprosthesis without a supporting stent caninclude a deposited thin film formed of a selected alloy and one or morepolymer layers to enhance radial and/or longitudinal strength. Inembodiments, the deposited metallic film is in the shape of a tube ofsubstantially uniform thickness. The metallic film can include a patternof polymer layers or strands.

In the embodiment shown, endoprosthesis 100 has a generally tubularshape. In some embodiments, however, the endoprosthesis (or stent body52 or tubular member 54 individually) has or includes other shapes suchas conical, oblate, and branched. The endoprosthesis may have a closedend to form, e.g., a basket shape. Thin films, discussed above, composedof Ni—Ti-strength additive alloys and/or with modified microstructures,can be used in other applications. Examples include baskets, filters,catheters, guidewires, and medical balloons, such as an angioplastyballoon.

Other examples of endoprostheses including a thin film as well asrelated systems and methods are described in U.S. provisional patentapplication No. 60/549,287, filed Mar. 2, 2004, which application isincorporated herein by reference.

An endoprosthesis may include a cover disposed externally to a frameworkas shown and/or internally of a framework. Endoprostheses having a coverincluding, e.g., a deposited thin film, disposed internally of aframework are described in U.S. patent application Ser. No. 11/025,464,titled MEDICAL DEVICES INCLUDING METALLIC FILMS AND METHODS FOR MAKINGSAME, and filed concurrently herewith, which application is incorporatedherein by reference.

An endoprosthesis may include features to enhance a flexibility of theendoprosthesis as described in U.S. patent application Ser. No.11/025,158, titled MEDICAL DEVICES INCLUDING METALLIC FILMS AND METHODSFOR MAKING SAME, and filed Dec. 29, 2004, which application isincorporated herein by reference.

The composition and/or fabrication method of a deposited thin film of anendoprosthesis may include features that enhance a strength or toughnessof the film as described in U.S. patent application Ser. No. 11/025,860,titled MEDICAL DEVICES INCLUDING METALLIC FILMS AND METHODS FOR MAKINGSAME, and filed Dec. 29, 2004, which application is incorporated hereinby reference.

An endoprosthesis may include one or more filaments, e.g., wires,adapted to enhance mechanical properties of a deposited thin film asdescribed in U.S. patent application Ser. No. 11/025,684, titled MEDICALDEVICES INCLUDING METALLIC FILMS AND METHODS FOR MAKING SAME, and filedDec. 29, 2004, which application is incorporated herein by reference.

Methods for loading an endoprosthesis into a delivery device and systemsfor delivering an endoprosthesis to a treatment site are described inU.S. patent application Ser. No. 11/025,660, titled MEDICAL DEVICESINCLUDING METALLIC FILMS AND METHODS FOR LOADING AND DEPLOYING SAME,filed Dec. 29, 2004, which application is incorporated herein byreference.

All publications, references, applications, and patents referred toherein are incorporated by reference in their entirety.

Other embodiments are within the claims.

1. An endoprosthesis, comprising: first and second tubular frameworksspaced apart by a degradable central portion and defining an interiorand an exterior, the tubular frameworks configured to, upon deploymentwithin a body passage, exert a radially expansive force against the bodypassage sufficient to retain the endoprosthesis with respect to the bodypassage, the degradable central portion configured to, upon deploymentwithin the body passage, initially reduce a flow of blood between theinterior and exterior of the endoprosthesis and, subsequent todeployment, degrade over time providing increased flow of blood betweenthe interior and exterior of the endoprosthesis; and a depositedmetallic film generally coextensive with at least a portion of at leastone of the frameworks.
 2. The endoprosthesis of claim 1, wherein themetallic film comprises nickel and titanium.
 3. The endoprosthesis ofclaim 1, wherein the metallic film has a thickness of less than about 50μm.
 4. The endoprosthesis of claim 1, wherein a different depositedmetallic film is generally coextensive with at least a portion of eachof the first and second frameworks.
 5. The endoprosthesis of claim 1,wherein the first and second frameworks are only connected by thedegradable central portion.
 6. The endoprosthesis of claim 1, furthercomprising a deposited metallic film connects the first and secondframeworks.
 7. An endoprosthesis, comprising: a generally tubulardeposited metallic film comprising first and second ends and at leastone fenestration located therebetween, the at least one fenestrationhaving an area sufficient to pass a microcatheter; and a degradablelayer obstructing the fenestration, the degradable layer configured to,upon deployment of the endoprosthesis within a body passage, degradethereby opening the fenestration to provide an area sufficient to allowpassage of a microcatheter.
 8. The endoprosthesis of claim 7, whereinthe fenestration has an area of at least 2 mm².
 9. The endoprosthesis ofclaim 7, wherein the fenestration has an area sufficient to pass a 1.7french catheter.
 10. The endoprosthesis of claim 7, wherein the metallicfilm comprises nickel and titanium.
 11. The endoprosthesis of claim 10,wherein the metallic film has a thickness of less than about 50 μm. 12.A generally tubular endoprosthesis defining an interior and an exterior,the endoprosthesis comprising: a tubular framework; a deposited metallicfilm covering the framework, the deposited metallic film comprising aplurality of fenestrations; and a degradable polymer layer extendingaround one or both of the film and the framework, the degradable polymerlayer configured to, upon deployment within a body passage, initiallylimit passage of liquid between the interior of the endoprosthesis andthe exterior of the endoprosthesis along a path including thefenestrations.
 13. The endoprosthesis of claim 12, wherein the metallicfilm comprises nickel and titanium.
 14. The endoprosthesis of claim 12,wherein the metallic film has a thickness of less than about 50 μm. 15.The endoprosthesis of claim 12, wherein the film comprises at leastabout 100 fenestrations.
 16. The endoprosthesis of claim 15, wherein thedegradable layer is configured to, upon deployment of the endoprosthesiswithin the body passage, degrade thereby allowing increasing passage offluid between the interior of the endoprosthesis and the exterior of theendoprosthesis along a path including the fenestrations.
 17. Theendoprosthesis of claim 1, wherein the metallic film has a thickness ofabout 4-35 μm.
 18. The endoprosthesis of claim 10, wherein the metallicfilm has a thickness of about 4-35 μm.
 19. The endoprosthesis of claim13, wherein the metallic film has a thickness of about 4-35 μm.
 20. Theendoprosthesis of claim 1, wherein the first and second tubularframeworks each have a plurality of struts, and wherein at least some ofthe struts crimp about a portion of the central portion to attach thefirst and second tubular frameworks to the central portion.
 21. Theendoprosthesis of claim 1, further comprising a plurality of radiopaquemarkers configured to define boundaries between the central portion andthe first and second tubular frameworks.
 22. The endoprosthesis of claim1, wherein the central portion comprises fenestrations.
 23. Theendoprosthesis of claim 1, wherein the central portion is configured torelease a pharmaceutically active compound during degradation.
 24. Theendoprosthesis of claim 1, wherein the central portion comprises firstand second portions, the first and second portions having differentdegradation lifetimes.
 25. The endoprosthesis of claim 7, wherein theendoprosthesis further includes markers configured to indicate anorientation of the plurality of fenestrations.
 26. The endoprosthesis ofclaim 16, wherein the degradable layer is configured to releasetherapeutic agents during degradation.